Its not good to see someone in a deep shit like yours. You know in work place women gets sexual advances from male, and even if not, still what she says, others will believe that. If she says that you didnot promote as you asked for a fuck and you denied, people will believe that, again if she gets a promotion and doesnot give you a promised fuck, you cant complain on that.
People like you, if were working for me, I would suggest them to talk to the supervisor, also based on the supervisor's suggestion, put something in written with HR. Thats the best way to save your own ass. If you haven't discussed with your supervisor, you are making a mistake.
Whatever you do, be absolutely sure you are not spoiling your company's money. Giving a raise that someone deserve on performance ground is okay, but someone has a monetary issue doesnot justify. Dont get too close to people to know what one's personal financial status is.
I am no saint and I had number of sweet encounters with my female colleagues, but not for a single occaisson that was free or do any favour. I made sure my money goes, but I wont allow my company's money for my pleasure or foolishness. If someone needs money that much, I will have sex and pay. But not by promotion and raise. Thats only for the performers who deserves.
I am really curious which city or company you work on that gives 20% raise. The city I work, having a steady job is the best benefit, a zero increment still is acceptable to people because the job is there.